396 LIMESTONE OF PENA.S NEGRAS. 



as subordinate to the conglomerate (evidently of tertiary 

 formation) of the Barigon and of the mountain of the 

 oastle of Cumana, because a little to the north of that castle 

 I had found shelves of hardened clay containing lamellar 

 gypsum inclosed in the tertiary strata. I believed that the 

 muriatiferous clay might alternate with the calcareous conglo- 

 merate of Barigon; and near the fishermen's huts situated 

 opposite Macanao, conglomerate rocks appeared to me to 

 pierce through the strata of clay. During a second excur- 

 sion to Maniquarez and the aluminiferous slates of Chapa- 

 ruparu, the connexion between tertiary strata and bituminous 

 clay seemed to me somewhat problematical. I examined 

 more particularly the Penas Negras near the Cerro de la 

 Vela, E.S.E. of the ruined castle of Araya. The limestone 

 of the Penas is compact, bluish grey, and almost destitute 

 of petrifactions. It appeared to me to be much more ancient 

 than the tertiary conglomerate of Barigon, and I saw it 

 covering, in concordant position, a slaty clay, somewhat 

 analogous to muriatiferous clay. I was greatly interested in 

 comparing this latter formation with the strata of carbu- 

 retted marl contained in the Alpine limestone of Cumanacoa. 

 According to the opinions now most generally received, the 

 rock of the Penas Negras may be considered as representing 

 muschelkalk (limestone of Gottingen) ; and the saliferous 

 and bituminous clay of Araya, as representing variegated 

 sandstone ; but these problems can only be solved when the 

 mines of those countries are worked. Those geologists who 

 are of opinion that the gem-salt of Italy penetrates into a 

 stratum above the Jura limestone, and even the chalk, may be 

 led to mistake the limestone of the Penas Negras for one of 

 the strata of compact limestone without grains of quartz 

 and petrifactions, which are frequently found amidst the 

 tertiary conglomerate of Barigon and of the Castillo de 

 Cumana ; the saliferous clay of Araya would appear to them 

 analogous to the plastic clay of Paris,* or to the clayey 

 shelves (dief et tourtia) of secondary sandstone with lignites, 

 containing salt-springs, in Belgium and Westphalia. How- 

 ever difficult it may be to distinguish separately the strata 

 of marl and clay belonging to variegated sandstone, muschel- 



* Tertiary sandstone with lignites, or molassus of Argovia. 



